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Multiplexing using TLC5951

Robert Airley
Prodigy 30 points
Other Parts Discussed in Thread: TLC59213A, TLC5951, TLC5944, TLC5924

Hi there,

I intend to use a TLC5951 as part of an RGB LED display. The screen would be made up of 8x8 pixel LED modules, each containing 64 RGB LEDs. The are connected internally in a common anode configuration. Basically, I would like to know if it is possible to use this chip to multiplex 8 rows of LEDs? This would mean that after every GSClk cycle, the next row of LED data would be loaded. Do you think this is a plausible solution? If not, do you have any other IC which may be suited to the job? I plan to use a TLC59213A or similar IC to source current and select the row.

Thanks

  • 0
    TI__Guru 59595 points

    Hello Robert,

    If you have an RGB LED array where all LEDs are connected together with the anode, time multiplexing the rows is not possible. For time multiplexing the rows, you need the anodes of one row connected together and each row then connected to one pin because then you could use a part like TLC59213A to connect the LED supply to just one row and each column to one output of TLC5951. Like in this figure:

    If all anodes are connected together, I do not see a possibility how to time-multiplex the rows.

    If you have common anode per row and the processor you are using for the communication is able to deliver the data in a high enough speed, it should be possible. Maybe TLC5924 or TLC5944 would be the better decision for time-multiplexed systems because they include pre-charge FETs that overcome the ghosting effect of LEDs with the cathode at the same OUTx pin.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 30 points

    Hi,

    Thanks for the reply. I meant 1 common anode per row, sorry. The layout of the LEDs is as shown in this datasheet:
    http://www.noodlehed.com/ebay/datasheets/GTM2088ARGB-21.pdf 

    Do you think the pre-charge FET version would make a drastic difference? The fact that they are only available with 16 channels makes it somewhat awkward to design with so I would rather avoid that if at all possible. I am considering using 3 8 channel PWM chips now as I would be able to shift data into them at a greater speed.

    Regards,

    Robert Airley 

  • 0 in reply to Robert Airley
    TI__Guru 59595 points

    Hello Robert,

    To be honest, I do not expect a drastic difference. It should work with TLC5951 as well, but this depends for sure on the picture update speed and the content of your pictures.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 190 points

    Hi. Thanks for your helpful comment. I'm wondering if you have something beefier than the TLC59213A, perhaps something that can dish out up to 7 amps per line for 8 lines (one at a time). I'm using around 64 LEDs per row. Must not be an all-in-one. Thanks!

  • 0 in reply to Steven Gutierrez
    Prodigy 30 points

    Hi everybody, I wanna know what you did. I'm gonna do the same project and I will be grateful if you can help me. Thank you mate. Cheers.

  • 0 in reply to Lautaro Guzman
    Prodigy 30 points

    Hi there!

    In the end, due to time constraints and the fact prototyping would have taken slightly longer with the IC package for the TLC5951, I opted to use 3 8-channel driver ICs that were available in DIP packages. I thought about it a lot and see no reason it wouldn't be possible. Please let us know how you get on though!